If they provide some level of stocking and quality control, they can. Dropshippers arbitrating between amazon and aliexpress don't really provide much of that.
What about insurance brokers? Or travel brokers? They don't have stock. Intermediaries (sort of) inherently create quality control via having a better perspective on the market than any single supplier can, and through pressuring individual suppliers via their own large-scale buying/selling activities.
E.g. if a dropshipper is selling mobile phone covers at scale, and stops using supplier x because the poor quality is affecting the dropshipper's brand, this puts more pressure on the supplier than if individual end-users stopped buying their products. Same applies to all brokers. They glean great power over suppliers in this fashion, while improving the experience for end-users (prime example: Amazon).
That isn't what happens though. Quality control with foreign suppliers is very difficult. A bad supplier with a bad name will disappear and come back with a new name. The shops are small and there are an enormous amount of them so there is very little what you might call reputation capital. Find people with experience sourcing products in China and get them to tell you stories.
